1. Field of the Invention
The present invention relates to a piezoelectric element and a liquid discharge head, and more particular, to a lead-free piezoelectric element including an oriented piezoelectric film.
2. Description of the Related Art
A piezoelectric element is typically formed of a bulk-shaped or film-shaped piezoelectric material including a lower electrode and an upper electrode.
As a piezoelectric material, ABO3 type ceramics such as lead zirconate titanate (hereinafter referred to as “PZT”) is generally used. However, PZT contains lead at an A-site of a perovskite skeleton. Therefore, the environmental impact of the lead component is considered to be a problem. In order to address this problem, a piezoelectric material and a piezoelectric element each using a lead-free perovskite-type metal oxide have been proposed.
For example, as a piezoelectric material formed of a lead-free perovskite-type oxide, “Chemistry of Materials” 2006, Vol. 18, No. 21, pp. 4987-4989 describes Bi(Zn0.5Ti0.5)O3. However, although the Bi(Zn0.5Ti0.5)O3 is theoretically expected to have excellent piezoelectric performance, it is difficult to polarize the Bi(Zn0.5Ti0.5)O3 due to its high Curie temperature, and hence the piezoelectric performance thereof has not been clarified. Further, there has yet been no report of successful synthesis of film-shaped Bi(Zn0.5Ti0.5)O3.
There have been proposed a piezoelectric material containing BiFeO3 as a main component as another piezoelectric material formed of the lead-free perovskite-type oxide, and a piezoelectric element using the piezoelectric material. For example, Japanese Patent Application Laid-Open No. 2007-287739 discloses a BiFeO3-based piezoelectric material containing La in an A-site and a piezoelectric element using the piezoelectric material. BiFeO3 is a satisfactory ferroelectric substance, and is reported to exhibit a large remnant polarization at low temperature. However, there remains a problem in that sufficient piezoelectric strain cannot be obtained from BiFeO3.
Further, “Chemistry of Materials” 2007, Vol. 19, No. 26, pp. 6385-6390 discloses a BiAlO3 piezoelectric material obtained by a high-pressure synthesis method. However, the piezoelectric performance of BiAlO3 has also not reached a practically applicable range yet.